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SE7Yf BY~ ~ .5-95 :10~09PM ; 0 ~ 303 832 8106;# 3/ 6 <br />The extent of surface deformation (subsidence) was calculated <br />using the computer model. The coal extraction ratio is set at a <br />lower limit of 75 percent for room and pillar mining. The model <br />will not accept a lower extraction ratio although the actual <br />extraction was 31 percent (attachment z). The model predicts the <br />zero subsidence line to be located 98 feet from the Tatum home <br />(attachment 3). This would put the Tatum home outside of the <br />zone of influence of subsidence associated with the room and <br />pillar mining in the first north portion of the mine. The above <br />calculation was based upon a distance from the Tatum home to the <br />edge of the panel of 35o ft, an overburden height of 455 ft, and <br />25 percent hardrock in the overburden. These are very <br />conservative numbers for the purposes of subsidence calculation <br />and would result in an over prediction of a subsidence zone. <br />During the investigation no subsidence features were noted on the <br />grounfl between the Tatum home and.the underground workings. The <br />pasture between the residence. and. the mine showed no signs of <br />surface deformation.. The .railroad tracks 650 feet to the <br />southwest of the Tatum home are located directly over the area of <br />the maximum predicated subsidence for the mine (-3.61 feet). The <br />tracks, drainage ditch, and cut bank showed no signs of <br />subsidence or surface deformation. <br />Considering the calculated safety factor of 2.5 (based on after <br />mining conditions), the overprediction of coal-extraction ratio <br />(75 percent assumed for modeling-31 percent actual), and no <br />visual observations of surface deformation directly over the mine <br />(the railroad track being one of the best indicators of surface <br />deformation), there is little likelihood that there has been <br />subsidence associated with the first north operation of the <br />Golden Eagle Ming that would have affectefl the Tatum home. <br />Micha F. nth <br />Chief, P~y ical Sciences Branch <br />Office of Surface Mining <br />Attachments <br />TATUMRPT.MIR <br />